Various techniques are known in the art for allowing a mobile unit, such as a mobile telephone, to communicate with a communications device, such as a hardwired telephone or another mobile unit. First generation personal communications networks required that a caller communications device know the current location of a callee mobile unit in order to successfully setup a call. Proposals for second generation personal communications networks require a mobile unit to perform two operations upon its entry into a new geographical area. First, the mobile unit must register at a visitor location register (VLR) and second, the mobile unit must update the contents of its home location register (HLR) to reflect its new location. As a travelling mobile unit moves into and out of different geographic areas, the required registering and updating operations would cause a tremendous increase in signalling traffic and would also be inconvenient.
In order to setup a call to a mobile unit using the proposed VLR/HLR technique, the network would first look at the mobile unit's HLR to find its current location. Then the network would send signalling information to that location and wait for a paging response from the mobile unit. When the network receives the paging response, it would setup a call from the originating caller to an access point of the callee mobile unit. Such a call setup technique would incur significant delays.